1. Field of the Invention
This invention relates a novel preparation process of nitroguanidine derivatives.
The process of the present invention is very useful upon preparation of a compound employed as an agricultural chemical (particularly, an insecticide) or an intermediate therefor.
2. Description of the Related Art
It is well known that certain nitroguanidine derivatives are useful as an agricultural chemical (particularly an insecticide) or intermediate therefor (Japanese Patent Laid-Open Nos. 288860/1990, 109374/1991, 157308/1991, 179448/1995).
Preparation processes of a di-substituted nitroguanidine as follows are known.
(1) A process of hydrolyzing a 1,3,5-tri-substituted 2-nitroiminohexahydro-1,3,5-triazine in the presence of an acid (Japanese Patent Laid-Open Nos. 291267/1991, 330049/1992). PA1 (1) A preparation process based on hydrolysis is accompanied with the drawbacks that owing to the existence of water or an acid in the reaction system, crystallization or purification cannot be carried out easily, and inorganic salts formed by neutralization are inevitably mixed in the system, which requires an additional cumbersome operation such as silica gel purification. The process of the present invention, on the other hand, does not need such a troublesome operation. PA1 (2) A solubility of a nitroguanidine derivative in an aqueous phase increases under high acid conditions upon neutralization with an acid, which lowers an extraction ratio or crystallization yield. When the reaction mixture becomes nearly alkaline or neutral by neutralization, a triazine derivative which is a raw material is reproduced, which causes a reduction in a yield or purity. It is therefore necessary to carry out severe pH control upon neutralization. Thus, the conventional process based on hydrolysis is markedly troublesome. The process of the present invention makes it possible to omit the pH control.
Reaction Formula (1) ##STR3## (2) A process of preparing via a certain isothiourea (Japanese Patent Laid-Open No. 9173/1993)
Reaction Formula (2) ##STR4## (3) A process of preparing via a certain dithiocarbamic acid derivative (Japanese Patent Laid-Open Nos. 120054/1992, 74158/1992).
Reaction Formula (3) ##STR5## (4) A process of preparing via a 1,2-di-substituted-3-nitroisothiourea (Japanese Patent Laid-Open No. 288860/1990).
Reaction Formula (4) ##STR6## (5) A process of alkylating a mono-substituted nitroguanidine directly (Japanese Patent Application No. 15814/1996).
Reaction Formula (5) ##STR7##
As described above, only the above process (1) is known as a process for preparing a di-substituted nitroguanidine by using 1,3,5-tri-substituted-2-nitroiminohexahydrotriazine as a raw material, but it is a process based on a hydrolytic reaction with an acid.
A nitroguanidine derivative is well known to have a high water solubility. In addition, a nitroguanidine tends to have higher water solubility under acid conditions than under neutral conditions. When the reaction is effected in the presence of water or an acid, a reduction in a crystallization yield or a reduction in an extraction ratio therefore occurs upon the isolating operation, which tends to make the operation troublesome.
If neutralization is conducted in order to suppress such a reduction, a triazine derivative is produced by the reverse reaction, which makes the operation more trouble-some.